The present invention relates to a toner carrier incorporated in a developing device of an image forming apparatus, and a method of producing the same.
An electronic copier, printer, facsimile transceiver or similar image forming apparatus of the type forming an electrostatic latent image on an image carrier and developing it to produce a toner image is conventional. It is a common practice with this type of apparatus to use a developing device operable with a one component developer, i.e., a toner with or without an auxiliary agent added thereto. Specifically, a toner carrier in the form of a roller or a sleeve transports the toner to a developing region where it faces the image carrier. The toner develops a latent image electrostatically formed on the image carrier to produce a corresponding toner image. This type of developing device promotes easy management and miniature construction, compared to a developing device operable with a two component developer including a carrier. However, with the device using a one component developer, it is difficult to deposit a sufficient amount of toner on the toner carrier and convey it to the developing region. Therefore, it is likely that the mount of toner available for development is short, lowering the density of the resulting toner image.
In light of this, there has been proposed a developing device which selectively deposits a charge on the surface of a toner carrier to generate numerous microfields near the surface of the toner carrier, causes a great amount of toner to deposit on the toner carrier due to the microfields, and develops an electrostatic latent image by such a toner, as disclosed in Japanese Patent Application No. 275061/1990 by way of example. With this type of developing device, it is possible to cause the toner carrier to carry a great amount of sufficiently charged toner thereon due to the microfields and convey it to the developing region, whereby a high quality toner image is insured. Various methods of producing a toner carrier applicable to such a developing device have also been proposed in the past. For example, a method disclosed in Japanese Patent Application 88650/1990 consists in spraying metal particles onto the surface of a conductive base, forming a dielectric coating on the metal particles, hardening the coating, and then grinding the surface of the coating to cause the conductive surfaces of the metal particles and the dielectric substance to appear on the periphery of the resulting toner carrier. However, the conventional toner carriers and methods of producing them are not practicable without resorting to a great number of steps for the production and, therefore, high cost.